1. Field of the Invention!
This invention relates to an apparatus for controlling the opening of a throttle valve for adjusting the volume of intake air for the engine of an automobile.
2. Description of the Prior Art!
FIG. 6 shows a throttle controller disclosed by Laid- open Japanese Patent Application No. Hei 3-141841. In FIG. 6, reference numeral 1 denotes an accelerator which turns in a direction shown by an arrow W from an initial position shown by a solid line by an unshown force in the direction shown by the arrow W, turns in a direction opposite to the direction shown by the arrow W by an unshown spring force when the force in the direction shown by the arrow W decreases and returns to the original position by the spring force when the force is removed. Numeral 2 represents an accelerator operation amount detection means which comprises a first accelerator sensor 2a and a second accelerator sensor 2b. The first and second accelerator sensors 2a and 2b output individual signals corresponding to the operation amount of the accelerator 1 from the initial position of the accelerator 1 to a control unit 12 incorporating a microcomputer. Numeral 3 denotes an accelerator switch for detecting whether the accelerator is in operation, which is turned on to output an ON signal to the control unit 12 when the accelerator 1 is away from its initial position and is turned off to output an OFF signal to the control unit 12 when the accelerator 1 is located at its initial position. Numeral 4 is an engine mounted on an automobile, 5 an engine speed sensor which outputs a signal corresponding to an engine speed to the control unit 12, 6 a car speed sensor mounted on the automobile which outputs a signal corresponding to the driving speed of the automobile to the control unit 12, and 7 a suction pipe which introduces air purified by an unshown air filter to the engine 4. Numeral 8 represents a throttle valve incorporated in the suction pipe 7 at a predetermined position, which turns around a valve axis 8a from a fully closed position shown by a solid line at which the volume of intake air is reduced to an extent that an engine stall occurs toward a fully opened position shown by a dotted line at which the volume of intake air is maximal or turns from the fully opened position toward the fully closed position to adjust the volume of intake air for the engine 4. Numeral 9 represents a throttle actuator, provided external to the suction pipe 7, for driving the throttle valve 8 to open at a rotation angle based on the fully closed position in response to a signal output from the control unit 12, and 10 a throttle opening sensor, provided external to the suction pipe 7, for detecting the opening of the throttle valve 8 and outputting a signal corresponding to the detected opening to the control unit 12. Reference numeral 11 represents a main switch mounted on the automobile, which starts an unshown starter motor mounted on the automobile by supplying power from an unshown battery to start driving the engine 4 when an unshown key plate is inserted into a key hole 11a and turned from an off position 11b to an IG position 11d through an AAC position 11c to turn on an ignition switch at the IG position 11d. The control unit 12 comprises a throttle opening control means 13, which is activated with power supplied from the battery when the key plate inserted into the key hole 11a of the main switch 11 reaches the ACC position 11c, to control the opening of the throttle valve 8 electrically in accordance with a program prestored in an unshown memory incorporated in the control unit 12. The control unit 12 further comprises a valve fixation diagnosis means 23 which determines electrically whether the throttle valve 8 is fixed at a fully closed position in accordance with the program prestored in the memory.
A description is subsequently given of the operation of the car throttle controller of FIG. 6. When the starter motor is started by inserting the key plate into the key hole 11a of the main switch 11 without operation of the accelerator 1, the throttle opening control means 13 opens the throttle valve 8 to a position where the volume of air required for the start of the engine 4 is supplied to the engine 4 from its fully closed position through the throttle actuator 9 based on a calculated target throttle opening. When the driver steps on the accelerator 1 after the engine 4 is started, the first and second accelerator sensors 2a and 2b output individual signals corresponding to the operation amount of the accelerator 1 to the control unit 12. The throttle opening control means 13 calculates an average value of the operation amounts of the accelerator 1 from the first and second accelerator sensors 2a and 2b, calculates a target throttle opening by inserting into an operation expression preset in the throttle opening control means 13 such data as the calculated average value, an engine speed from the engine speed sensor 5, a car speed from the car speed sensor 6 and the amount of an electrical load on the battery, and outputs an opening control signal for nullifying the difference between the target throttle opening and the throttle opening detected by the throttle opening sensor 10 to the throttle actuator 9. Thereby, the throttle actuator 9 is supplied with power corresponding to the opening control signal from the battery to control the opening of the throttle valve 8 to the target throttle opening. Thus, the intention of the driver is transmitted to the throttle opening control means 13 by the first and second accelerator sensors 2a and 2b through the operation amount of the accelerator 1 and the opening of the throttle valve 8 is electrically controlled to the target throttle opening by the throttle actuator 9 to adjust the output of the engine 4. When a voltage detection value representing a detected throttle opening from the throttle opening sensor 8 falls below a voltage decision value corresponding to the fully closed position of the throttle valve 8 preset in the valve fixation diagnosis means while the accelerator switch 3 is on, the valve fixation diagnosis means 23 concludes that the throttle valve 8 is fixed at a fully closed position. Then, according to the result of this judgment, the valve fixation diagnosis means 23 causes unshown spring force to be applied to the throttle valve 8 to return it to a neutral opening position.
The throttle controller of the prior art has the disadvantage that the throttle valve is determined to be fixed at the fully closed position when the target throttle opening is small and the opening of the throttle valve 8 is controlled to a position close to the fully closed position. That is concluded that the throttle valve is fixed at the fully closed position even though it is under control. This is because it is determined that the throttle valve 8 is fixed at a fully closed position based on one judging condition that a voltage detection value indicative of the detected throttle opening falls below a voltage decision value.